Decyl alcohol mixtures, phthalic esters obtainable therefrom and their use as placticizers

ABSTRACT

Mixtures of isomeric decyl alcohols prepared by hydroformylation of mixtures of butene-1 and butene-2 in two stages to give aldehyde mixtures, and condensation of the aldehyde mixtures to form an aldol mixture, followed by separation and hydrogenation. The first stage of the hydroformylation proceeds in the presence of rhodium catalysts dissolved in water, the second stage in the presence of cobalt catalysts homogeneously dissolved in the reaction medium. The mixture of isomeric decyl alcohols, when esterified with phthalic acid, yields a mixture of isomeric decyl phthalates which are useful as plasticizers.

This is a division of application Ser. No. 08/311,561, filed Sep. 23,1994.

This Application claims the benefit of the priority of GermanApplication P 43 33 324.9, filed Sep. 30, 1993.

The invention relates to mixtures of isomeric decyl alcohols, a processfor their preparation, the phthalic esters obtained from these alcohols,and their use as plasticizers.

BACKGROUND OF THE INVENTION

Esters of phthalic acid are used to a great extent as plasticizers, inparticular for polyvinylchloride. The alcohol components customarilyused are primary aliphatic alcohols having 8 to 10 carbon atoms, amongwhich 2-ethylhexanol currently is of the greatest importance. Phthalicesters of alcohols having less than 8 carbon atoms in the molecule leadto plasticizers having good gelling power. However, their relativelyhigh volatility is a disadvantage. Phthalic esters which are derivedfrom primary aliphatic alcohols having more than 10 carbon atoms, incontrast, gel more slowly and are less cold-resistant.

The properties of the phthalic ester plasticizers are influenced by thebranching of the carbon chain, in addition to the size of the alcoholmolecules. Thus, alcohols with a low degree of branching give esterplasticizers of high cold flexibility. Substantially linear alcoholshaving 8 to 10 carbon atoms in the molecule are therefore gainingincreasing importance as the alcohol component of phthalic esters. Aprecondition for their use is that they be available in large amountsand at a reasonable cost.

According to German Patent 2 855 421, phthalates of 9 carbon alcohols,useful as plasticizers, are obtained by hydroformylation of 8 carbonolefins, hydrogenation of the reaction product, and esterification ofthe resultant 9 carbon alcohols with phthalic anhydride. 3% to 20% byweight of the starting olefins have an isobutane skeleton in eachmolecule chain, less than 3% by weight of the olefins has a quaternarycarbon, and more than 90% by weight of the total amount of olefins ispresent as n-octenes, monomethylheptenes, and dimethylhexenes. Inaddition, the weight ratio of the total amount of n-octenes andmonomethylheptenes to the dimethylhexenes is more than 0.8.

Phthalic esters of 10 carbon alcohols are the subject matter of EuropeanPatent Application 03 66 089. The alcohols used for the esterificationare in the form of a mixture produced by hydroformylation of a butenefraction, aldol condensation of the resulting aldehyde mixture, andsubsequent hydrogenation. The hydroformylation step, according to theprocess description, is not subject to any restrictions. Thus, not onlycobalt, but also rhodium, can be used as catalyst, and the addition ofan organic compound of trivalent phosphorus is not excluded.

Another way to obtain didecyl phthalic mixtures is described in EuropeanPatent Application 04 24 767. The esters are prepared by a multi-stageprocess by dimerization of butene mixtures, hydroformylation, andhydrogenation of the resulting octene mixture to a nonanol mixture,dehydration of the nonanol mixture to form a nonene mixture, followed byhydroformylation and hydrogenation of the nonene mixture to form adecanol mixture.

The known processes do not satisfy all of the requirements, botheconomic and technical, which are made of a process to be carried out onan industrial scale. The starting materials are either not available insufficient quantities, or they are not inexpensive, or the conversion ofthe starting materials into the desired alcohols is associated withexcessively complex (and hence costly) processes. In multi-stageprocesses, which include the hydroformylation of butene, then-valeraldehyde content, in particular, of the hydroformylation productshould be as high as possible, to promote the formation ofstraight-chain alcohols or alcohols which are only slightly branched.

SUMMARY OF THE INVENTION

The object was, therefore, to develop a process which not only startsfrom raw materials which are inexpensive and readily available, butwhich can also be converted in a scientifically simple manner into thedesired straight-chain or only slightly branched alcohols.

The isomeric decyl alcohols of the present invention are obtained in twostages. First, olefin mixtures containing butene-1 and butene-2 arehydroformylated, the reaction proceeding in the first stage in aheterogeneous reaction system using, as catalysts, rhodium compoundscontaining complexed water-soluble phosphines. The first stage iscarried out at temperatures of 70° to 150° C. and pressures of 0.4 to 30MPa. In the second stage, the reaction of the product of the first stagetakes place in a homogeneous phase, in the presence of cobalt compoundsas catalysts, at temperatures of 130° to 180° C. and pressures of 8 to30 MPa to form aldehyde mixtures. Separation and combination of theresulting aldehyde mixtures from the hydroformylation stages,condensation of the combined aldehyde mixture to form an aldol mixture,and separating and hydrogenating the aldol mixture provide the desiredmixture of isomeric decyl alcohols.

DETAILED DESCRIPTION OF THE INVENTION

The 1-butene- and 2-butene-containing starting mixtures for thepreparation of the isomeric decyl alcohols according to the inventionare necessarily produced in large quantities as refinery by-products inthe production of motor vehicle fuels and in the preparation of ethyleneby thermal cracking of high molecular weight hydrocarbons. They areisolated from the 4 carbon cracking cuts of the pyrolysis product byextraction of the butadiene with a selective solvent and subsequentseparation of the isobutene, preferably by conversion into methyltert-butyl ether. The n-butene-containing product separated from thepyrolysis product which has been freed of butadiene is termed raffinateI. If, in addition, the isobutene is separated with the n-butene, theproduct is called raffinate II. Instead of extracting butadiene, it canbe partially hydrogenated in the 4 carbon cracking cut to give butenes.After separating out the i-butene, a butene-1/butene-2 mixture isobtained which is particularly suitable for further processing to 10carbon alcohols. Finally, attempts have been made recently tohydrogenate the separated butadiene to form butane and return it to thecracking vessel to increase the yield of ethylene and propylene.

According to the invention, mixtures containing butene-1 and butene-2,e.g. in the form of raffinate II, but which may also be of differentorigin and composition, are hydroformylated in two stages. In the firststage, butene-1 preferably reacts to form a mixture which predominantlycomprises n-valeraldehyde and, in a lesser amount, i-valeraldehyde. Thereaction proceeds under conditions which largely exclude anisomerization of the butene-1 to give butene-2. In the second stage, thebutene-2 is hydroformylated to give a mixture of n-valeraldehyde andi-valeraldehyde.

The first stage of the hydroformylation is carried out as aheterogeneous reaction in a two-phase system, a conversion which isdescribed, e.g. in DE-C 26 27 354. This process is characterized by thepresence of an organic phase, which contains the starting olefins andthe reaction product, and an aqueous phase, in which the catalyst isdissolved. The catalysts which are used are water-soluble rhodiumcomplex compounds which contain water-soluble phosphines as ligands. Thephosphines include, in particular, triarylphosphines,trialkylphosphines, and arylated or alkylated diphosphines, the organicradicals of which are substituted by sulfonic acid groups or carboxylgroups. Their preparation is disclosed by, e.g. DE-C 26 27 354 andGerman Democratic Republic patent 259 194.

The butene reaction proceeds at temperatures of 70° to 150° C.,preferably 100° to 130° C. and at pressures of from 0.4 to 30, inparticular 1 to 10, MPa with water gas which contains carbon monoxideand hydrogen in a volume ratio of 1:10 to 10:1. The rhodiumconcentration is 20 to 1000 ppm by weight, preferably 50 to 500 ppm byweight, based on the aqueous catalyst solution. Per mole of rhodium, 4to 100 mol of water-soluble phosphine are used. The volume ratio ofaqueous to organic phase is 0.1 to 10:1.

The conversion of butene per unit of time is markedly increased if aphase transfer reagent (solubilizer) is added to the aqueous catalystsolution. It alters the physical properties of the interfaces betweenthe two liquid phases and facilitates the transfer of the organicreactant into the aqueous catalyst phase.

Known solubilizers are compounds whose hydrophilic groups are anionic,cationic, or nonionic. The anionic compounds include sodium salts,potassium salts, or ammonium salts of carboxylic acids having 8 to 20carbon atoms, in particular of saturated fatty acids having 12 to 18carbon atoms, as well as alkyl sulfates, alkylbenzenesulfonates, andalkylbenzenephosphonates. Examples of cationic solubilizers aretetraalkylammonium and N-alkylpyridinium salts. The nonionic phasetransfer reagants cannot dissociate into ions in aqueous solution. Theyinclude alkyl polyethylene glycols, alkylphenyl polyethylene glycols,alkylolamides of fatty acids, and trialkylamine oxides. Finally,ampholytes such as aminocarboxylic acids, betaines, and sulfobetainesare also useful as solubilizers.

Cationic solubilizers, in particular of the formula [A--N(R¹ R² R³)]⁺ E⁻have proven to be useful. A is a straight or branched chain alkylradical having 6 to 25 carbon atoms, R¹, R², and R³ are the same ordifferent and are straight or branched chain alkyl radicals having 1 to5 carbon atoms, and E is an anion, in particular sulfate,tetrafluoroborate, acetate, methosulfate, benzenesulfonate,alkylbenzenesulfonate, toluenesulfonate, lactate, or citrate.

In the first reaction stage, hydroformylation of the butene-1 containedin the butene mixture to n-valeraldehyde should be as complete aspossible. A decisive criterion for the termination of the reaction isthe increased production of i-valeraldehyde. Its content should be lessthan 10% by weight (based on the aldehyde mixture). Thus, for a butene-1conversion rate which, depending on the reaction parameters selected, isup to 95%, the aldehyde mixture contains at least 90% n-valeraldehyde,the rest is i-valeraldehyde.

Olefins which did not react in the first stage (predominantly butene-2)leave the reactor together with carbon monoxide, hydrogen, and thebutane formed by hydrogenation of the olefins. The gas mixture issubjected to a pressure of 8 to 30 MPa without intermediate treatmentand is further reacted in a homogeneous phase in a second reaction stageat temperatures of 130° to 180° C. The catalyst used is cobalt. It isfed to the reaction mixture as the metal, expediently in a finelydivided form, or better as a compound soluble in organic media, e.g. ascobalt carbonyl or as a salt of a carboxylic acid, such as2-ethylhexanoic acid. The cobalt concentration is 0.1% to 3% by weight,preferably 0.6% to 1.0% by weight, based on the butenes introduced intothe second reaction stage. The presence of a solvent such as toluene,xylene, or tetrahydrofuran is not absolutely necessary, because itsfunction can be taken over by the starting material and the reactionproduct. The water gas has the same composition as in the first reactionstep. Depending on the reaction conditions, up to 99% of the olefin usedis converted into n- and i-valeraldehyde.

After termination of each hydroformylation, the aldehyde mixtures ofeach of the reaction steps are separated off from their respectivecatalysts, from the unreacted starting materials, and from the remainingproducts. In the case of the heterogeneous reaction (first stage), thisis carried out by simple phase separation. For the reaction inhomogeneous phase, i.e. the second stage of the novel process, thecatalyst is removed from the depressurized or partly depressurizedreaction product by known processes, e.g. by treatment with steam (cf.DE-C-3 032 252).

The aldol condensation of the combined aldehyde mixtures of the firstand second hydroformylation stages is carried out in a conventionalmanner under the action of basic catalysts. Pretreatment of thealdehydes, e.g. special purification, is not required. Catalysts whichare used include alkali metal carbonates or alkali metal hydroxides, inparticular compounds of sodium, potassium, or amines, preferablytertiary amines, such as triethylamine, tri-n-propylamine, andtri-n-butylamine. The reaction is carried out at temperatures of 60° to160° C., in particular 80° to 130° C., under atmospheric or elevatedpressure up to about 1 MPa. The reaction time is from a few minutes upto several hours and is dependent, in particular, on the catalyst typeand reaction temperature. Owing to its higher reaction velocity,n-valeraldehyde preferentially aldolizes with itself or with isomericvaleraldehydes to give decenals; any condensation of2-methylvaleraldehyde or isovaleraldehyde, in contrast, is so minimal asto be insignificant.

The aldehyde mixture obtained by the foregoing condensation is thenhydrogenated to give the desired decyl alcohol mixture. The addition ofhydrogen proceeds in a known manner in the presence of catalysts. Thosewhich are suitable are, for example, hydrogenation catalysts based onnickel, chromium, or copper. The hydrogenation temperature isconventionally between 100° and 180° C. and the pressure between 1 and10 MPa. The decyl alcohol mixture is purified by distillation and isespecially suitable as the alcohol component of phthalic esters whichare to be used as plasticizers.

The preparation of the phthalic esters is known [cf. Ullmann,Encyclopadie der Technischen Chemie [Encyclopedia of IndustrialChemistry] (1979), Vol. 18, pages 536 et seq.]. Phthalic anhydride isexpediently reacted in one stage with the decyl alcohol mixture in themolar ratio 1:2. The reaction velocity can be increased by catalystsand/or by increasing the reaction temperature. In order to shift theequilibrium in the direction of ester formation, it is necessary toremove the resulting water from the reaction mixture. The phthalatesobtained from the decyl alcohol mixture according to the invention aredistinguished as plasticizers by excellent cold properties.

While only a limited number of specific embodiments of the presentinvention have been expressly disclosed, it is, nonetheless, to bebroadly construed and not to be limited except by the character of theclaims appended hereto.

What we claim is:
 1. An ester mixture comprising products of thereaction of phthalic acid or phthalic anhydride, with an alcohol mixtureof isomeric decyl alcohols which is the product of hydroformylation ofan olefinic mixture containing butene-1 and butene-2, saidhydroformylation being carried out in a first stage and a secondstage,said first stage comprising a first hydroformylation of saidolefinic mixture in a heterogeneous reaction system at a firsttemperature of 70° to 150° C. and under a first pressure of 0.4 to 30MPa, in the presence of an aqueous solution of a first catalyst, saidfirst catalyst comprising at least one rhodium compound and at least onewater-soluble phosphine, to form a first reaction mixture containing afirst aldehyde mixture, separation of said first aldehyde mixture fromsaid first reaction mixture leaving a residue which contains butene-2,said second stage comprising a second hydroformylation of said residuein a homogeneous reaction system at a second temperature of 130° to 180°C. and under a second pressure of 8 to 30 MPa, in the presence of acobalt catalyst, to form a second reaction mixture containing a secondaldehyde mixture, said second aldehyde mixture being separated from saidsecond reaction mixture, and combined with said first aldehyde mixtureto form a combined aldehyde mixture, condensed to form a third reactionmixture containing an aldol mixture, separation of said aldol mixturefrom said third reaction mixture, and hydrogenation of said aldolmixture forming said alcohol mixture.
 2. The ester mixture of claim 1wherein said first temperature is 100° to 130° C., and said firstpressure is 1 to 10 MPa.
 3. The ester mixture of claim 1 wherein saidfirst catalyst is present in a first catalyst amount of 20 to 1000 ppmby weight, based on said aqueous solution.
 4. The ester mixture of claim3 wherein said first catalyst amount is 50 to 500 ppm by weight.
 5. Theester mixture of claim 1 wherein said first catalyst, per mol ofrhodium, contains 4 to 100 mols of said water soluble phosphine.
 6. Theester mixture of claim 1 wherein said aqueous solution contains atransfer reagent.
 7. The ester mixture of claim 1 wherein said cobaltcatalyst comprises 0.1% to 3% by weight of cobalt, based on said butenesin said second hydroformylation.
 8. The ester mixture of claim 6 whereinsaid cobalt catalyst comprises 0.6% to 1.0% by weight of cobalt.
 9. Aplasticizer comprising a phthalate ester of an alcohol mixture ofisomeric decyl alcohols which alcohol mixture is the product ofhydroformylation of an olefinic mixture containing butene-1 andbutene-2, said hydroformylation being carried out in a first stage and asecond stage,said first stage comprising a first hydroformylation ofsaid olefin mixture in a heterogeneous reaction system at a firsttemperature of 70° to 150° C. and under a first pressure of 0.4 to 30MPa in the presence of an aqueous solution of a first catalyst, saidfirst catalyst comprising at least one rhodium compound and at least onewater-soluble phosphine, to form a first reaction mixture containing afirst aldehyde mixture, separation of said first aldehyde mixture fromsaid first reaction mixture leaving a residue which contains butene-2,said second stage comprising a second hydroformylation of said residuein a homogeneous reaction system at a second temperature of 130° to 180°C. and under a second pressure of 8 to 30 MPa in the presence of acobalt catalyst to form a second reaction mixture containing a secondaldehyde mixture, said second aldehyde mixture being separated from saidsecond reaction mixture, and combined with said first aldehyde mixtureto form a combined aldehyde mixture, said combined aldehyde mixturebeing condensed to form a third reaction mixture containing an aldolmixture, separation of said aldol mixture from said third reactionmixture, and hydrogenation of said aldol mixture forming said alcoholmixture.
 10. The plasticizer of claim 9 wherein said first temperatureis 100° to 130° C. and said first pressure is 1 to 10 MPa.
 11. Theplasticizer of claim 9 wherein said first catalyst is present in a firstcatalyst amount of 20 to 1000 ppm by weight, based on said aqueoussolution.
 12. The plasticizer of claim 11 wherein said first catalystamount is 50 to 500 ppm by weight.
 13. The plasticizer of claim 9wherein said first catalyst, per mol of rhodium, contains 4 to 100 molof said water-soluble phosphine.
 14. The plasticizer of claim 9 whereinsaid aqueous solution contains a transfer agent.
 15. The plasticizer ofclaim 9 wherein said cobalt catalyst comprises 0.1% to 3% by weight ofcobalt, based on said butenes in said second hydroformylation.
 16. Theplasticizer of claim 15 wherein said cobalt catalyst comprises 0.6% to1.0% by weight of cobalt.
 17. A method of plasticizing a resincomprising mixing therewith the plasticizer of claim 9.